Certain motor vehicles are fitted with devices for providing assistance in driving and having the purpose of improving the road holding of the vehicle. Such driving assistance devices can be classified into two categories. A first category comprises devices that act in active manner on the behavior of the vehicle to take the place of the driver in the event of a dangerous situation. This first category includes, for example: active systems of the type that prevent the brakes locking (ABS) or of the stability management type (ESP). The second category comprises devices that provide information for the purpose of warning the driver that the driver is in a situation that is potentially dangerous.
The invention relates more particularly to devices of this second category and that serve to estimate a risk of a lack of connection with the ground for the vehicle, and to inform the driver.
In order to estimate this risk, it is possible to use numerous known parameters, in particular outside temperature. A temperature sensor fitted to a vehicle can warn the driver whenever the outside temperature drops below a certain threshold at which it is possible that ice will form on the road.
This estimate of the risk of a lack of connection with the ground is simple but does not enable accurate and reliable results to be obtained. This estimate assumes that below a certain temperature, the road is icy, but it does not verify that assumption. Thus, it is common for the vehicle to trigger a warning even though there is no real risk of a lack of connection with the ground. Furthermore, in certain situations, measuring temperature will not detect a risk of a lack of connection with the ground even when one exists, for example when there is oil on the road or when the tires are very worn.
Parameters other than temperature can be used for estimating the risk of a loss of connection with the ground, but none of them is capable of providing an estimate that is effective and reliable under all circumstances.